Generally, conventional power steering apparatuses for a vehicle include a hydraulic power steering apparatus using a hydraulic pressure of a hydraulic pump. However, an electric power steering apparatus using an electric power motor has gradually prevailed since the 1990s.
In the conventional hydraulic power steering apparatus, the hydraulic pump serving as a power source supplementing the power is actuated by an engine, so that the energy is always consumed regardless of rotation of a steering wheel. While, in the electric power steering apparatus, when the steering wheel rotates and the torque is generated, the motor actuated by an electric energy supplies the steering assistant power. Therefore, the electric power steering apparatus can improve the energy efficiency of a vehicle rather than the hydraulic power steering apparatus.
In general, an electronic control brake system is a system for efficiently preventing a slip of a vehicle so as to obtain powerful and stable braking force. The electronic controlled brake system includes an Anti-Lock Brake System (ABS) preventing a slip of the wheel upon braking, a Brake Traction Control System (BTCS) preventing a slip of a driving wheel upon suddenly accelerating or accidentally speeding up of a vehicle, and an Electronic Stability Program (ESP) controlling a hydraulic pressure of a brake through combining the ABS with the BTCS so as to stably maintain the driving conditions of a vehicle.
The conventional ESP is an apparatus by which a vehicle itself brakes or controls the engine torque so that it enables a driver to escape from danger in a dangerous driving situation. In other words, the ABS works only when a driver directly steps on the brake of a vehicle and only during a braking process, while the ESP can find the optimum driving of a vehicle by itself, even when a user does not step on the brake.
Meanwhile, in an operating method of the common ESP, a steering angle sensor, a G-sensor for detecting an acceleration in a vertical direction of a vehicle, and a Yaw sensor for sensing inward inclination occurring upon a circular driving of a vehicle sense a rotation speed of a wheel, yawing moment, an angle of a steering wheel, a stepping force of an accelerator, or the like, and then an Electronic Control Unit (ECU) analyzes them. According to an analyzed result, the ECU optimally controls the braking force and the driving force applied to each wheel so as to obtain driving safety of a vehicle.
The conventional steering angle sensor has been mainly employed in the ESP sensing a movement of a vehicle. However, the conventional steering angle sensor has been recently used in a steering system, such as Electric Power Steering (EPS). The steering angle sensor employed in the EPS performs a function of transmitting a steering angle signal measuring a rotation angle of the steering wheel rotated by a driver's operation to the ECU.
Generally, the EPS system employing the steering angle sensor checks if a fail exists in the steering angle signal received from the steering angle sensor. If it does, the EPS system employs a method for operating a fail-safe logic. However, there is a disadvantage that only the conventional method cannot accurately determine if the fail exists in the steering angle signal. Therefore, a method of detecting a malfunction of the steering angle sensor or the fail in the steering angle signal using the rotation direction of the motor in the EPS system employing the steering angle sensor has been required. However, the method still has not been provided.